The present invention relates a composite puffed borax particulate material and to a means for producing same. More particularly, the instant invention concerns a puffed borax material having on its surface particles or grains of a metallic oxide compound and to a means of producing such a material.
Sodium tetraborate (Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O) is a free-flowing solid crystal containing five molecules of water per mole of borate. When the crystal is heated rapidly under controlled conditions, the water is vaporized in a process which causes the formation of a low density puffed particle characterized by a high degree of internal and external porosity. An apparatus and process for preparing such puffed borax, or a borax matrix, is described in U.S. Pat. No. 3,454,357. The density of the particles depends upon the manner in which borate is heated and may vary from 55 pounds per cubic foot to as low as about 2 pounds per cubic foot.
This material has a number of uses. Particularly, it is well known that this borax matrix can absorb organic solvents such as trichloroethylene. In many cases as much as 50% of a liquid may be adsorbed while still giving the appearance of a dry free-flowing solid. Solids, too, have been deposited on a puffed borax matrix. However, this has been accomplished by applying them to the borax matrix while the solid is in the molten state or by depositing them by evaporation from solution in the presence of puffed borax, the liquid phase being a solvent for the material to be loaded, but not for borax.
The present invention is based, at least in part, upon the discovery that certain metal powders, particularly refractory metal oxides, are readily adsorbed and retained on to the surface as well as within the interstices or pores of a puffed borax matrix. It is an object of this invention therefore to provide a particle comprising a matrix of puffed borax, with the matrix having on its surface and in its interstices thereof grains of a metal-oxygen compound.
Another object of this invention is to provide a particle as described above wherein the metal-oxygen compound is a metal oxide.
A further object is to provide a particle wherein the puffed borax matrix with adsorbed powder has a bulk density of between about 4 and about 65 pounds per cubic foot and the supporting borax matrix has a bulk density of from about 4 to about 30 pounds per cubic foot.
A still further object is to provide a particle whrein the puffed borax matrix comprises between about 10 to about 99% of the weight of the particle.
Additional objects of the invention are to provide a particle wherein the metal oxide compound is antimony oxide.
Another object is to provide a particle wherein the adsorbed powder has a grain size from about 0.1 to about 100 microns.
Another object of this invention is the provision of a process to prepare the loaded matrix particles described hereinbefore.
The low density puffed borax particles, where the interior supporting walls have become thin, are fragile and susceptible to breakdown by handling. When the metal oxides have filled these pores, however, it has been found that the friability of the puffed borax matrix is reduced. Moreover, the addition of puffed borax to an ordinarily dusty material, such as antimony oxide, produces a mass of greatly reduced dustiness.
The compositions of this invention find a number of industrial applications where both borax and oxides are parts of basic formulations. One such area is in the ceramic industry where metal oxides are used for pigmentation. Another very important application is in plastics and cellulosic products where fire retardancy and smoke suppression specifications must be achieved. These specifications generally require that antimony oxide be included in combination with a halogen-containing material to impart fire retardancy, and this property can be further enhanced, along with some degree of smoke suppression, if borates, phosphates, and certain metal oxides, such as zinc and molybdenum, are included.
Metal oxides are generally produced by calcination which, in most cases, results in very fine and dusty products. This property presents handling and health hazard problems which are greatly minimized by the use of this invention provided borax is also a desirable ingredient of the resultant formulation.